The yaw system for a wind turbine consists of a yaw brake and a yaw drive, which directs the nacelle of the wind turbine in the direction of the wind to maximize the efficiency of the wind power system and reduces the fatigue load acting on the wind turbine. As a result of structural analysis of the slip and holding states of the yaw brake for a 4 MW class wind turbine, this paper confirmed that the safety rate of yaw brake parts was 1.35 or higher, which is safe. In addition, fatigue analysis was performed using the Markov matrix selected as the condition of load duration distribution (LDD) data, and cumulative fatigue damage was calculated using the Goodman diagram and the Minor cumulative damage law. As a result of the yaw brake fatigue analysis, it was found that the total damage calculated for each part was 0.324, 0.000231, and 0.696449, which were very safe. The natural frequency of the yaw brake was calculated and risk speed analysis was performed. As a result, it was found that no resonance occurred within the operating speed range.

As the demand for offshore wind energy grows, accurate prediction of monopile behavior under lateral loading is important for the design of safe foundations. To evaluate the lateral responses of monopiles, this research investigated three analysis approaches, namely, a 6×6 stiffness matrix model, a beam-spring model using p-y curves, and a 3D finite element method. Validation of the three methods was carried out using the results from centrifuge model tests. It was observed that the beam-spring model, based on PISA p-y curves, matched the experimental results most accurately, with just a 3% deviation. The FEM came close with a 5% error but required significantly more time and resources. The stiffness matrix approach, on the other hand, showed limited performance, likely due to its simplified linear assumptions. A sensitivity analysis of the beam-spring model revealed that variations in the estimated shear modulus from SPT N-values can substantially affect prediction outcomes. These findings underscore the importance of reliable geotechnical data and engineering judgment when applying simplified models in the design of monopile foundations.

The design of mooring systems for floating offshore wind systems is often hindered by the limited availability of detailed turbine information, as manufacturers typically withhold such data to protect proprietary knowledge. This limitation affects the accuracy of dynamic behavior analyses and can have significant implications for the safety and cost-effectiveness of projects. To address this issue, this study proposes and validates a simplified model that predicts the extreme mooring line loads of FOWS using only thrust data, which is generally available, without relying on detailed turbine specifications. Comparative analyses were conducted between the simplified model and a detailed model in various design load cases. The results show that the simplified model effectively captures both the maximum mooring line tension and the overall load response trends in a manner consistent with the detailed model. In particular, the prediction error was minimal under parked turbine conditions, indicating high accuracy. Furthermore, the simplified model proved useful in identifying critical environmental conditions that induce peak loading. In conclusion, the proposed simplified model is considered a practical tool for evaluating extreme mooring loads during the early design stages, especially when access to detailed turbine data is limited.

This study is a comparative study of the characteristics of design space approximation according to various meta-models and design sensitivity evaluation using orthogonal array experiments for the Fairlead chain stopper (FCS), a detachable mooring system developed for a 10 MW-class floating offshore wind turbine. This study proposes a design methodology based on orthogonal array experiments that enables the efficient exploration of the best design case and generation of highly accurate meta-models. Thickness dimensions of the main components of the FCS are applied as design variables, while the output responses are defined as weight and strength performances. The quantitative effect of each design variable on the output responses is evaluated from the design sensitivity analysis. Various meta-models are generated, including the response surface methodology (RSM) model, Kriging, Chebyshev orthogonal polynomial (COP), and radial basis function neural network (RBFN). From the comparison of meta-model accuracy, the most appropriate meta-model is confirmed for the exploration of the FCS design space. Among the meta-models, RBFN represents accuracy for the design approximation of the FCS.

Offshore wind power systems rely on grounding electrodes for lightning protection and electrical stability, but these electrodes face severe corrosion due to continuous exposure to seawater. In this study, five candidate materials (BeCu, Zn, Cu, SUS304, and Al) were subjected to galvanostatic accelerated corrosion tests to quantitatively evaluate their corrosion characteristics. The experimental results showed that higher current density led to greater corrosion damage in all samples. In particular, aluminum and copper exhibited very high corrosion rates and severe surface damage, indicating vulnerability in long-term performance. In contrast, the beryllium-copper alloy (BeCu) and stainless steel (SUS304) exhibited superior corrosion resistance, showing minimal weight loss and surface degradation under impressed current conditions. However, microscopic examination revealed the presence of localized deep pits on the SUS304 surface. As a result, BeCu is identified as the most reliable and durable candidate for grounding electrode applications. Zinc demonstrated moderate corrosion behavior, but the formation of protective zinc oxide layers under specific conditions contributed to partially mitigating the corrosion process. Overall, BeCu emerged as the best candidates for offshore wind grounding electrodes, whereas Al and Cu are less favorable due to their susceptibility to corrosion. This work provides a valuable basis for material selection to improve the stability and lifespan of offshore wind turbines. It also suggests that further research on long-term corrosion behavior in real marine environments and the combined application of corrosion protection technologies is necessary.

In this work, investigation on self-healing method of composite laminate structure was performed. Large structures, such as wind turbine blades, are vulnerable to damage. Wind turbine blades are manufactured using composite materials. In this study, domestic and international research trends on damage self-healing techniques for composite structures were analyzed. And also, the self-healing application method of composite blades for wind power generation system was studied. The application of self-healing method after damage was studied during the structural design process.

As wind turbines grow larger, blade certification testing becomes increasingly challenging. In edgewise fatigue testing, inertia generators have been developed to apply sufficient bending moment in the inboard section, including the blade root. However, frictional forces in the inertia generator's rotating part cause significant damping, which increases the energy required for excitation. This leads to reduced energy efficiency, necessitating larger exciters to test ultra-large blades. This study identified friction as the primary damping source and proposed compensating the pendulum weight to reduce it. Quantitative evaluation of the damping rate confirmed that weight compensation improves excitation capability. Consequently, edgewise fatigue testing can be conducted more efficiently and reliably using the improved inertia generator with weight compensation.

Offshore wind development in Korea has been delayed due to complex permitting procedures and conflicts among developers, fishers, and government ministries. This study proposes a site selection framework using GIS-based exclusion analysis that integrates marine spatial data produced by government and public agencies. The framework considers primary factors such as water depth and wind speed, and additional factors including offshore wind permit status, metocean instruments, fishing effort density, and total catch. Ten scenarios were developed by combining turbine types (fixed-bottom and floating) with planning priorities (economic feasibility vs. social acceptance). The results show that scenarios prioritizing economic feasibility yield broader candidate areas, while those incorporating social acceptance significantly reduce site availability. Differentiated weighting of fishing effort density and total catch illustrates how site selection outcomes shift depending on whether emphasis is placed on spatial fishing intensity or fisheries productivity. The framework is expandable as a web-based platform to support multi-stakeholder pre-consultation and is expected to contribute as a technical foundation for the Site Information System mandated by the Offshore Wind Power Act (Articles 12 and 14).

This paper compares the wave-induced responses of an offshore wind turbine in towing and installation. Encounter wave frequency is higher and the period is shorter in towing condition with ship speed than in installation without speed. So, hydro-dynamic behavior is different although the sea state is the same. A 10 MW offshore wind turbine with a supporting tower and three legs was analyzed to compare wave-induced responses in towing and installation. Floating body motions and section forces at the tower and leg bases were calculated by solving dynamic coupled equations in the time domain. Wave forces were calculated by superposition of force RAO and wave spectrum. The encounter wave spectrum was applied in the case of towing. The pitch motion of the floating body and bending moments and shear forces at tower and leg bases were larger in the case of installation, while axial forces at the tower and leg bases were larger in the case of towing because heave acceleration was larger.

In this study, the motion response of the substructure of an offshore wind farm was evaluated under design environmental conditions during the installation procedure. The substructure, designed to reduce the Levelized Cost of Energy (LCOE), consists of three pontoons with the tower located at the center. Due to its relatively high center of gravity compared with conventional offshore structures and its small restoring moment, it is important to understand its motion characteristics during installation. Furthermore, because towing efficiency using tugboats is a critical factor, the resistance of the platform's substructure with different towing configurations is also of importance. The motion response and resistance were investigated through model tests conducted at KRISO's Ocean Engineering Basin in Daejeon, Korea. The evaluation focused on the initial installation stage, specifically, the towing condition to the designated site prior to lowering the legs, under combined ocean environmental conditions. Three different towing configurations were also examined to determine the most effective arrangement in terms of both motion response and resistance.

The objective of this study is to improve the capacity factor of offshore wind power generation and improve its economic feasibility through performance improvement of wind turbines, primarily based on the analysis of actual operation and management data from the Southwest Sea Offshore Wind Demonstration Site (with a capacity of 60 MW, hereinafter referred to as the "Demonstration Site"). According to the research findings, the capacity factor of wind turbines is largely influenced by the wind conditions of the wind farm and the performance of the turbines. The performance analysis of the turbines was conducted through an examination of the failure rates of major turbine components. To reduce these failure rates and improve the capacity factor, it was found necessary to comprehensively implement O amp;M technologies such as condition-based maintenance and predictive maintenance, establish replacement criteria for major components and predict failures in advance, and improve the facilities of key components.

This study proposes a reinfusion-based repair method for unimpregnated interlaminar defects that occur during the infusion process of pultruded CFRP spar caps. Small-diameter holes were drilled into pultruded CFRP laminates to locally inject resin into unimpregnated interlaminar defect regions. Phased array ultrasonic testing confirmed effective resin infiltration in most areas, although minor voids remained near the boundary between original and repaired regions. Interlaminar shear tests conducted on specimens from the intact, repaired, and boundary zones showed comparable strength levels. Additionally, CT imaging revealed that failure occurred within the CFRP plies rather than along the repaired interfaces. These findings demonstrate that the proposed repair method successfully restores the structural integrity of defective spar caps.

This study presents a numerical analysis of a 15 MW floating offshore wind turbine equipped with a disconnectable mooring system. To evaluate the dynamic response characteristics, a fully coupled time-domain simulation was performed using in-house code developed by the Korea Research Institute of Ships and Ocean Engineering (KRISO). The code combines a potential-flow-based hydrodynamic model with a finite-element-based nonlinear mooring line model to account for wave-structure-mooring interactions. Numerical results were validated against model tests conducted in the KRISO deep ocean engineering basin under identical environmental conditions. Static offset curves, natural periods, and free decay responses were compared and showed good agreement with experimental measurements. Furthermore, dynamic simulations under the ultimate limit state condition (DLC 6.2) reproduced the surge, heave, pitch motions, and mooring line tensions with deviations generally within 5-8% of the model test data. These findings confirm that the in-house code can reliably capture the nonlinear behavior of disconnectable mooring systems and provide accurate predictions of coupled dynamic responses. The validated framework offers a practical tool for the design and safety assessment of large-scale floating offshore wind turbines with innovative mooring configurations.

The adoption of a jack-up–type substructure offers a practical route to markedly reduce the installation cost of fixed-bottom offshore wind turbines. Major modules are pre-assembled onshore, wet-towed to the site by tugs, and self-installed by an onboard jacking system, reducing reliance on heavy-lift vessels and shortening weather windows. To evaluate structural safety, a global analysis was performed within a Load and Resistance Factor Design (LRFD) framework in accordance with DNV guidance to verify global strength, plating buckling, and overturning stability under governing ultimate limit state (ULS) and accidental limit state (ALS) conditions.

To lower the levelized cost of energy (LCOE), KOMS Inc. developed the K-Wind substructure. It is critical to ensure the structural integrity of this substructure, since it experiences fluctuating loads from the wind turbine tower during operation. This study evaluated the fatigue damage of the substructure according to following steps. First, an integrated load analysis was conducted using Deeplines Wind software to obtain the load data. Based on these data, the number of cycles for each load range were determined by rainflow cycle counting. Nominal stress was calculated from a global structural analysis using unit loads. This was combined with the stress concentration factor (SCF) to determine the hot-spot stress. Finally, fatigue damage was calculated by applying the hot-spot stress and load distribution to Palmgren-Miner's rule.

Calculating the hydrodynamic force acting on a floating platform is essential to assess its dynamic behavior. Traditionally, such analyses for floating offshore oil and gas platforms have involved three-dimensional diffraction/radiation potential analysis to derive added mass coefficients, radiation damping coefficients, and wave exciting force coefficients in the frequency domain. These coefficients are then used to compute the dynamic response in the time domain, and the same procedure is typically applied to floating offshore wind turbine substructures. However, when the shape or dimensions of a floating platform change during the early design stage, the potential analysis must be repeated each time, which can delay the design process. This study investigates the use of a modified Morison's equation as a more efficient method to approximate the hydrodynamic force on a substructure without requiring potential analysis in the early design phase of floating offshore wind turbines. A procedure is proposed for determining the added mass coefficients and the Morison's equation correction that minimizes the errors relative to the results of potential analysis. To validate the proposed method, the dynamic response of a 15 MW floating offshore wind turbine was calculated using the modified Morison's equation. The results of this study demonstrate that applying the modified Morison's equation can predict wave loads at a level similar to that of diffraction/radiation potential analysis, which allows rapid estimation of the dynamic behavior of the floater in the early design stage.

This study investigates the critical issue of annual energy production losses caused by external wake effects in clustered offshore wind planning zones in Korea. This densification of wind farm locations leads to increased interactions between wakes of neighboring clusters, resulting in quantifiable annual energy losses, economic risks, and potential conflicts among stakeholders. Using the Shinan offshore wind cluster as a case study, this paper performs scenario-based quantitative simulations of external wake-induced losses and analyzes the resulting financial impacts based on the latest competitive bidding price caps. Furthermore, by benchmarking European (especially UK) legal, regulatory, and R&D practices, the study suggests improvements tailored for Korea, such as implementing inter-farm spacing requirements, mandating external wake impact assessments, expanding data-driven R&D efforts, and introducing conflict management schemes.